Obesity is associated with numerous co-morbidities, including cardiovascular disease, diabetes, hypertension and some cancers. Weight loss is difficult; therefore interventions to prevent the development of obesity are warranted. In this project we will evaluate the potential of resistance training (RT) to prevent the development of obesity in healthy, sedentary, overweight, young (18-25 yrs) college men and women, an accessible group at high risk for becoming obese. RT offers an innovative approach to obesity prevention that differs in concept from. Unlike aerobic exercise, RT results in a minimal increase in energy expenditure during exercise, but may result in significant increases in total daily energy expenditure resulting from increased resting metabolic rate (RMR) mainly as a result of increased fat-free mass (FFM). The efficacy of the RT protocols recommended as part of adult fitness programs to alter FFM and RMR is unknown. Therefore; this research project will determine the level of RT necessary to induce increases in muscle mass and RMR, which may, in turn be associated with weight maintenance or loss. All RT will be supervised and verified by the research team. We will compare changes in FFM and RMR elicited by 24 weeks of RT conducted as recommended by ACSM (1 set, 3 d/wk, resistance 8-12 repetitions maximum (RM), 9 exercises) with a higher intensity RT program (1 set, 3 d/wk, resistance 3-6 RM, 9 exercises) in a volunteer sample of 108 young adults (36 men, 72 women) matched on muscle mass and randomly assigned to the RT protocols or a non-exercise control condition within gender. Fat-free and muscle mass (DEXA), RMR (indirect calorimetry), and muscular strength (1-RM) will be assessed at baseline, and at 12 and 24 weeks. Dietary intake (24hr. recall) will be assessed monthly. If our pilot project proves successful, i.e., our RT program results in clinically significant increases in RMR, we will propose a larger and longer (18 m) randomized trial to assess the efficacy of RT for weight loss or prevention of weight gain. This trial will employ a complete energy balance model including detailed assessments of total energy intake and expenditure using state-of-the-science techniques (doublylabeled water, whole-room calorimetry, visual plate waste), and will investigate potential mechanisms, such as changes in protein turnover and sympathetic nervous system activity, that may be associated with increased RMR resulting from RT.